[Intel-wired-lan] [next-queue PATCH v2 2/5] net/sched: Fix accessing invalid dev_queue

[Jesus Sanchez-Palencia]

Hi,

On 09/30/2017 05:22 PM, Cong Wang wrote:
> On Fri, Sep 29, 2017 at 5:26 PM, Vinicius Costa Gomes
> <vinicius.gomes at intel.com> wrote:
>> From: Jesus Sanchez-Palencia <jesus.sanchez-palencia at intel.com>
>>
>> In qdisc_alloc() the dev_queue pointer was used without any checks being
>> performed. If qdisc_create() gets a null dev_queue pointer, it just
>> passes it along to qdisc_alloc(), leading to a crash. That happens if a
>> root qdisc implements select_queue() and returns a null dev_queue
>> pointer for an "invalid handle", for example.
> 
> Does it make sense to let mqprio_select_queue() always return
> non-NULL?
> 
> At least mq_select_queue() returns queue #0 as a fallback.

I had seen that, but my understanding was that for mqprio the inner qdiscs are
always related to one of the Tx netdev_queue per design. Returning any other
queue as a fallback seemed like going against that to me.

I'd rather keep this function as the patch is proposing, thus either returning
the correct netdev_queue for a given handle, or NULL as a way to flag that
something was 'wrong' with it. Returning queue #0 is misleading in that sense, imo.

What do you think?

Regards,
Jesus